This lesson is dedicated to two important circle formulas, the length of an arc of a circle (s=rθ) and the area of a sector of a disk (A=½r2θ). These will enable us to extend our ability to solve application problems.

Objectives

By the end of this topic you should know and be prepared to be tested on:

3.4.1 Use the arc length formula to find s, r, or theta.

3.4.2 Use the area of a sector formula to find A, r, or theta

3.4.3 Realize that theta in both of the above formulae is in radian measure only

READ THIS ARTICLE Radian Angular Measure which is an excerpt from Trigonometric Delights by Eli Maor, Princeton University Press, 1998. The article answers such questions as, "Why are there 360 degrees in a circle?", "Why are angles measured counterclockwise?", and "Why use radians over degrees?". Math majors are definitely encouraged to read the entire book (and everything else my Eli Maor, in my opinion).